Atomic layer etching of AL2O3 using a combination of plasma and vapor treatments

ABSTRACT

A method for performing atomic layer etching (ALE) on a substrate, including the following method operations: performing a surface modification operation on a surface of the substrate, the surface modification operation configured to convert at least one monolayer of the substrate surface to a modified layer; performing a removal operation on the substrate surface, the removal operation configured to remove the modified layer from the substrate surface, wherein removing the modified layer occurs via a ligand exchange reaction that is configured to volatilize the modified layer; performing, following the removal operation, a plasma treatment on the substrate surface, the plasma treatment configured to remove residues generated by the removal operation from the substrate surface, wherein the residues are volatilized by the plasma treatment; repeating the foregoing operations until a predefined thickness has been etched from the substrate surface.

FIELD OF THE INVENTION

Implementations of the present disclosure relate to atomic layer etching(ALE), and more specifically to ALE of aluminum oxide using acombination of plasma and vapor treatments.

DESCRIPTION OF THE RELATED ART

Conventional techniques of etching material on semiconductor substrateswith fine-tuned control over the uniformity and etch rate are limited.For example, reactive ion etch is conventionally used to etch materialson a semiconductor substrate during semiconductor processing and etchrates of materials etched using reactive ion etch are controlled bymodulating radio frequency plasma power and chemistry selection.However, a wafer plasma sheath forms at the top of the substrate, andthus ions from the plasma are typically accelerated onto the wafersurface to etch the substrate. This results in an anisotropic,directional etching process, which does not etch vertical and horizontalsurfaces of the material at the same rate. In addition, materialssubject to conventional etching processes may also be non-uniform. Usingconventional techniques often involves specific reactor design and/ormodification of feed-gas delivery and exhaustion as well as carefulmonitoring of temperature distribution of both chamber or reactor wallsand an electro-static chuck which may be part of a wafer holder capableof holding the wafer during processing to achieve high etch rateuniformity control, and which can result in less efficient and morecostly processing of substrates.

SUMMARY

In accordance with some implementations, a method for performing atomiclayer etching (ALE) on a substrate is provided, comprising: (a)performing a surface modification operation on a surface of thesubstrate, the surface modification operation configured to convert atleast one monolayer of the substrate surface to a modified layer; (b)performing a removal operation on the substrate surface, the removaloperation configured to remove the modified layer from the substratesurface, wherein removing the modified layer occurs via a ligandexchange reaction that is configured to volatilize the modified layer;(c) performing, following the removal operation, a plasma treatment onthe substrate surface, the plasma treatment configured to removeresidues generated by the removal operation from the substrate surface,wherein the residues are volatilized by the plasma treatment; (d)repeating operations (a) through (c) until a predefined thickness hasbeen etched from the substrate surface.

In some implementations, performing the surface modification operationincludes exposing the substrate surface to a fluorine-containing plasma,wherein the exposure to the fluorine-containing plasma is configured toconvert the at least one monolayer of the substrate surface to afluoride species.

In some implementations, the surface of the substrate includes a metal,metal oxide, metal nitride, metal phosphide, metal sulfide, or metalarsenide; wherein the exposure to the fluorine-containing plasma forms ametal fluoride.

In some implementations, exposing the surface of the substrate to thefluorine-containing plasma includes introducing a fluorine-containinggas into a chamber in which the substrate is disposed, and igniting aplasma.

In some implementations, the exposure to the fluorine-containing plasmais performed at a chamber pressure of about 10 to 500 mTorr, for aduration less than about 15 seconds.

In some implementations, performing the removal operation includesexposing the substrate surface to tin-(II) acetylacetonate (Sn(acac)₂)vapor, the exposure to the Sn(acac)₂ vapor being configured to exchangeacac ligands for fluorine atoms in the modified layer.

In some implementations, exposing the surface of the substrate to theSn(acac)₂ includes introducing the Sn(acac)₂ as a vapor into a chamberin which the substrate is disposed.

In some implementations, the exposure to the Sn(acac)₂ is performed fora duration of about 1 to 30 seconds.

In some implementations, performing the plasma treatment includesexposing the substrate surface to a hydrogen plasma, the exposure to thehydrogen plasma being configured to volatilize tin, tin fluoride or tinoxide residues on the surface of the substrate.

In some implementations, exposing the surface of the substrate to thehydrogen plasma includes introducing a hydrogen gas into a chamber inwhich the substrate is disposed, and igniting a plasma.

In some implementations, the exposure to the hydrogen plasma isperformed for a duration of about 1 to 30 seconds, typically, about 5seconds.

In some implementations, operation (a) is performed in a first chamber;operation (b) is performed in a second chamber.

In some implementations, operation (d) is performed in the firstchamber.

In some implementations, operation (d) is performed in a third chamber.

In accordance with some implementations, a method for performing atomiclayer etching (ALE) on a substrate is provided, comprising: (a)performing a surface modification operation on a surface of thesubstrate, the surface modification operation configured to convert atleast one monolayer of the substrate surface to a modified layer; (b)performing a removal operation on the substrate surface, the removaloperation configured to remove the modified layer from the substratesurface, wherein removing the modified layer occurs via a ligandexchange reaction that is configured to volatilize the modified layer;(c) repeating operations (a) and (b) for a predefined number of cycles;(d) performing, following operation (c), a plasma treatment on thesubstrate surface, the plasma treatment configured to remove residuesgenerated by the removal operation from the substrate surface, whereinthe residues are volatilized by the plasma treatment; (e) repeatingoperations (a) through (d) until a predefined thickness has been etchedfrom the substrate surface.

In some implementations, performing the surface modification operationincludes exposing the substrate surface to a fluorine-containing plasma,wherein the exposure to the fluorine-containing plasma is configured toconvert the at least one monolayer of the substrate surface to afluoride species; wherein performing the removal operation includesexposing the substrate surface to tin-(II) acetylacetonate (Sn(acac)₂)vapor, the exposure to the Sn(acac)₂ vapor being configured to exchangeacac ligands for fluorine atoms in the modified layer; whereinperforming the plasma treatment includes exposing the substrate surfaceto a hydrogen plasma, the exposure to the hydrogen plasma beingconfigured to volatilize tin, tin fluoride or tin oxide residues on thesurface of the substrate.

In some implementations, the surface of the substrate includes a metal,metal oxide, metal nitride, metal phosphide, metal sulfide, or metalarsenide; wherein the exposure to the fluorine-containing plasma forms ametal fluoride.

in some implementations, the exposure to the fluorine-containing plasmais performed at a chamber pressure of about 10 to 500 mTorr, for aduration less than about 15 seconds; wherein the exposure to theSn(acac)₂ is performed for a duration of about 1 to 30 seconds,typically, about 1 second; wherein the exposure to the hydrogen plasmais performed for a duration of about 1 to 30 seconds, typically about 5seconds.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F conceptually illustrate an ALE process sequence, inaccordance with implementations of the disclosure.

FIG. 2 illustrates a method for an ALE cycle, in accordance withimplementations of the disclosure.

FIG. 3 illustrates a process flow diagram for a method for performingALE, in accordance with implementations of the disclosure.

FIG. 4 conceptually illustrates an apparatus having multiple chambersfor performing ALE operations, in accordance with implementations of thedisclosure.

FIG. 5 illustrates a method in accordance with the embodiment of FIG. 3,but with the fluorine exposure and the Sn(acac)₂ exposure being repeateduntil n number of cycles has been reached, in accordance withimplementations of the disclosure.

FIG. 6 illustrates a cluster tool 600, in accordance withimplementations of the disclosure.

FIG. 7 illustrates an example chamber for performing ALE, in accordancewith implementations of the disclosure.

FIG. 8 shows a control module for controlling the systems describedabove, in accordance with implementations of the disclosure.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the presented embodiments. Thedisclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Provided herein are methods of performing isotropic atomic layer etching(ALE) of metal oxides (such as aluminum oxide (Al₂O₃)) via a ligandexchange mechanism involving a fluorine-containing plasma and atin-containing etchant. Methods described herein involve modifying asurface of the material to be etched using a fluorine-containing plasmaand exposing the modified surface to tin-(II) acetylacetonate(Sn(acac)₂) vapor to remove the material in a self-limiting manner. Aligand exchange reaction is sustained in a vapor deposition chamber withSn(acac)₂ vapor without plasma.

Atomic layer etching (ALE) is one approach for atomic scale control ofetching behavior. ALE is a type of cycling process. ALE is a techniquethat removes thin layers of material using sequential self-limitingreactions. Generally, ALE may be performed using any suitable technique.Examples of atomic layer etch techniques are described in U.S. Pat. No.8,883,028, issued on Nov. 11, 2014; and U.S. Pat. No. 8,808,561, issuedon Aug. 19, 2014, which are herein incorporated by reference forpurposes of describing example atomic layer etch and etching techniques.In various embodiments, ALE may be performed with plasma, or may beperformed thermally.

ALE may be done by a surface modification operation (i.e., chemisorptionby reactive chemistry on a substrate surface) followed by a removaloperation. Such operations may be repeated for a certain number ofcycles. During ALE, the reactive chemistry and the removal chemistry aredelivered separately to the substrate.

FIGS. 1A-1F conceptually illustrate an ALE process sequence, inaccordance with implementations of the disclosure.

Shown at FIG. 1A is a portion of a surface 100 of a substrate in anunmodified state. The outermost layer 102 of molecules/atoms of thesubstrate surface 100 are exposed for the ALE process. As shown at FIG.1B, a surface conversion/modification operation is performed to convertthe surface layer of the substrate to a functionalized state. Forexample, the surface layer is modified by exposure to a surfaceconversion reactant 104, which may adsorb or chemisorb on the surface.The surface conversion reactant can include molecules or low energyradicals in various implementations, which react with the surface layeratoms to effect the surface conversion step. The resulting surface layeris shown at FIG. 1C consisting of a functionalized outermost layer 106of molecules to enable subsequent ALE steps. As the reaction isself-limiting, only (or substantially only) the outermost layer of thesubstrate surface will undergo conversion. In some implementations, thissurface modification entails conversion of the surface species to ahalide. In some implementations, following the self-limiting surfaceconversion, the chamber is purged to remove any reaction byproducts orexcess surface conversion reactant.

Following the surface conversion operation, then as illustrated at FIG.1D, a ligand exchange reaction/operation is performed. In theillustrated implementation, the modified surface 106 of the substrate isexposed to a ligand containing reactant 108, which effects a ligandexchange reaction wherein the ligand containing reactant adsorbs on thesubstrate surface and transfers its ligands to the converted surfacespecies 106 which were formed during the earlier surfacemodification/conversion operation. The ligands bond with the modifiedsurface layer of molecules/atoms, forming a reaction product consistingof ligand substituted surface species 110 shown at FIG. 1E, which can bereleased.

As shown at FIG. 1F, desorption drives removal of the outermost layer ofsurface species 110 (the reaction product following the ligand exchangeoperation) from the substrate surface. In some implementations, therelease can be achieved by the application of thermal energy, which canbe applied simultaneous with the exposure to the ligand containingreactant or in a separate step.

The concept of an “ALE cycle” is relevant to the discussion of variousembodiments herein. Generally an ALE cycle is the minimum set ofoperations used to perform an etch process one time, such as etching amonolayer. The result of one cycle is that at least some of a film layeron a substrate surface is etched. Typically, an ALE cycle includes amodification operation to form a reactive layer, followed by a removaloperation to remove or etch only this modified layer. Modification maybe performed by using a chemisorption mechanism, deposition mechanism,top layer conversion mechanism, or extraction mechanism. The cycle mayinclude certain ancillary operations such as sweeping one of thereactants or byproducts. Generally, a cycle contains one instance of aunique sequence of operations. As an example, FIG. 2 illustrates amethod for an ALE cycle, including the following operations: (i)delivery of a reactant gas (operation 201), (ii) optional purging of thereactant gas from the chamber (operation 203), (iii) delivery of aremoval gas and an optional plasma (operation 205), and (iv) optionalpurging of the chamber (operation 207). Further description and examplesof ALE are described in U.S. patent application Ser. No. 14/696,254,filed on Apr. 24, 2015 and titled “INTEGRATING ATOMIC SCALE PROCESSES:ALD (ATOMIC LAYER DEPOSITION) AND ALE (ATOMIC LAYER ETCH),” which isincorporated herein by reference for purposes of describing atomic layeretch processes.

A process flow diagram for a method performed in accordance withdisclosed embodiments is provided in FIG. 3. During operations 301-307,an inert gas such as an argon gas may be continuously flowed in thebackground as a carrier gas.

In operation 301, a substrate including a material to be etched isexposed to a fluorine-containing plasma to modify the surface of thesubstrate.

The fluorine-containing plasma may be generated by introducing afluorine-containing gas and igniting a plasma. For example, in someembodiments, the fluorine-containing gas may be carbon tetrafluoride(CF₄), nitrogen trifluoride (NF₃), sulfur hexafluoride (SF₆), fluorine(F₂), or any fluorine-containing gas. In various embodiments, CF₄ may beintroduced with O₂ to generate an abundance of fluorine ions in theplasma to etch the substrate. In some embodiments, about 35% of thetotal flow of gases to the chamber to generate the fluorine-containingplasma is O₂ gas. Other fluorine-containing gases that include carbonmay be used in some embodiments when introduced with another gas toinhibit the formation of a carbide. For example, otherfluorine-containing gases may have the formula C_(x)H_(y)F_(z), where xmay be any integer greater than or equal to 1, y may be any integergreater than or equal to 0, and z may be any integer greater than orequal to 1. Examples include fluoroform (CHF₃) and difluoromethane(CH₂F₂). In some embodiments, the fluorine-containing gas may begenerated by vaporizing a fluorine-containing liquid.

In some embodiments, the substrate is not patterned. In variousembodiments, the substrate may be patterned. The substrate may include atransistor structure which may include an additional gate layer such asa blocking oxide or an etch stop layer. For example, the substrate mayinclude an aluminum oxide layer over a fin of a FinFET transistor. Insome embodiments, the substrate may include a 3D NAND structure with ametal oxide etch stop layer at the bottom of trenches formed in thestructure such that the metal oxide etch stop layer is the material tobe etched. In various embodiments, features on the substrate may have anaspect ratio between about 1.5:1 and about 5:1.

The plasma in operation 301 may be generated in situ or may be a remoteplasma. In many embodiments, the plasma is generated in situ to generatean inductively coupled plasma.

In various embodiments, the substrate includes a metal oxide, metalnitride, metal phosphide, metal sulfide, metal arsenide, or metal layerto be etched. Examples include aluminum oxide (Al₂O₃) and hafnium oxide.Note that in many embodiments, silicon-containing material (e.g.,silicon oxide, silicon nitride, silicon carbide, silicon, etc.) may notbe etched using disclosed embodiments, which contributes to achievingetch selectivity particularly when etching a material such as asacrificial gate oxide layer over a fin on a FinFET transistorstructure. Although it will be understood that disclosed embodiments maybe used to etch various materials, FIG. 1 will be described with respectto etching aluminum oxide.

In various embodiments, operation 301 may be performed without applyinga bias to allow isotropic modification of the substrate surface. Notethat although disclosed embodiments may be used to perform isotropicetch, an anisotropic etching process may also be performed usingdisclosed embodiments by applying a bias during operation 301. Theexample described herein with respect to FIG. 1 will be described forisotropically etching aluminum oxide.

Without being bound by a particular theory, during operation 301, ametal oxide surface such as an aluminum oxide surface, may befluorinated by the fluorine-containing plasma isotropically to modifythe surface of the aluminum oxide to form aluminum fluoride (e.g.,AlF₃). One or a few monolayers of the aluminum oxide surface may bemodified to form aluminum fluoride. The modification operation may belimited by the depth of diffusion. The substrate may be exposed to thefluorine-containing plasma at a chamber pressure between about 10 mTorrand about 100 mTorr, such as at about 20 mTorr for a duration less thanabout 15 seconds but greater than 0 seconds.

Note that in some embodiments, after performing operation 301, thechamber housing the substrate may not be purged. In some embodiments,the substrate may be purged.

In operation 303, the substrate is exposed to tin-(II) acetylacetonate(Sn(acac)₂) vapor. In various embodiments, Sn(acac)₂ may be vaporized inan external vaporizer prior to delivering the vapor to the substrate.

Without being bound by a particular theory, it is believed that when themodified AlF₃ surface is exposed to Sn(acac)₂ vapor, a ligand exchangereaction occurs such that one acac ligand on Sn(acac)₂ replaces onefluorine atom on a AlF₃ molecule, forming AlF₂(acac). AdditionalSn(acac)₂ and/or Sn(acac) may then react with AlF₂(acac) again twice toreplace the second and third fluorine atoms with (acac), resulting inAl(acac)₃, which is volatile and may thus be etched from the substrate.Since the ligand exchange reaction is theorized to have a faster etchrate in the top monolayer of AlF₃ (e.g., the first monolayer exposed tothe Sn(acac)₂ vapor), the reaction is self-limiting and some tin, tinfluoride, tin oxide, and Sn(acac)₂ may begin to build up on the surfaceof the material to be etched, thus blocking further etching of anymodified underlayers of AlF₃.

In various embodiments, operations 301 and 303 may be performed in thesame chamber. In operation 303, the plasma is turned off and thefluorine-containing gas flow may be turned off prior to turning on thevapor flow. Where the chamber is not purged prior to operation 303, thepresence of the fluorine-containing gas without a plasma may not affectthe etching mechanism. Rather, the fluorine-containing gas alone may beselected such that it does not react with the material to be etched as agas and also does not react with the vapor used in operation 303.

In some embodiments, operations 301 and 303 may be performed in separatechambers of the same apparatus. FIG. 4 conceptually illustrates anapparatus having multiple chambers for performing ALE operations, inaccordance with implementations of the disclosure. In variousembodiments, the substrate may be shuttled or moved between a firstchamber 401 for exposing to a fluorine-containing plasma in operation301 to a second chamber 403 for exposing to Sn(acac)₂ vapor. In someembodiments, the second chamber 403 is a vapor deposition chamber. Insome embodiments, the second chamber 403 is a modified chamber that doesnot include a plasma source. Note that movement or shuttling of thesubstrate between chambers may be performed without breaking vacuum.

In alternative embodiments, the substrate may be exposed to anotherchemical in vapor phase that is selective to the metal fluoride but doesnot react with the metal oxide. The chemical may include one or moreligands that, when reacted with a metal fluoride, generates a volatilecompound including the metal bonded to the ligand.

Operation 303 may be performed for a duration of about 1 second with thetemperature of the wafer holder or pedestal holding the wafer set to atemperature of about 200° C. In various embodiments, the chamberpressure at the end of the exposure to the Sn(acac)₂ vapor may be about20 mTorr.

In operation 305, the substrate may be exposed to a plasma treatment.Without being bound by a particular theory, it is believed thatoperation 305 is performed to volatilize tin, tin fluoride or tin oxidebuildup on the surface of the substrate, which can accumulate fromperforming operation 303. Exposing the substrate to hydrogen may formtin hydrates which are volatile at the chosen substrate temperature,which may then be pumped from the processing chamber. The substrate maybe exposed to the plasma treatment for a duration greater than 0 secondsand less than 5 seconds. The duration of plasma exposure may depend onthe amount of tin on the surface. For example, in some embodiments, theamount of tin may be determined by evaluating tin lines in an emissionspectrum. In some embodiments, the plasma may be turned off when the tinlines in an emission spectrum disappear. In some embodiments, thesubstrate is exposed to the plasma for about 5 seconds. In someembodiments, the substrate is exposed to the plasma for a durationgreater than about 5 seconds. In various embodiments, the plasmatreatment may include introducing a hydrogen gas and igniting a plasma.Operation 305 may be performed in the same chamber as in operation 301and 303. Note that although operation 305 may be performed by exposingthe substrate to hydrogen plasma, in some embodiments a differentchemistry may be used to remove tin or tin oxide buildup on the surfaceof the material to be etched. For example, in some embodiments, ammonia(NH₃) plasma may be used.

In some embodiments, operation 305 may be performed in a separatechamber. For example, in some embodiments, the substrate may be moved orshuttled to the first station/chamber 401 where operation 301 wasperformed, or may be moved or shuttled to a third station/chamber 405 toperform operation 305. Note that movement or shuttling of the substratebetween chambers may be performed without breaking vacuum.

In operation 307, it is determined whether the amount etched issufficient to achieve the desired amount to be etched. If the desiredremaining thickness has not yet been achieved, operations 301-305 may beoptionally repeated. Note that in some embodiments, operation 305 mayonly be performed every n cycles of performing operations 301 and 303,where n is an integer greater than or equal to 1. Where n is 1,operation 305 is performed in every cycle. In various embodiments,operation 305 is performed in every cycle. In another example, operation305 may be performed every 2 cycles of performing operations 301 and 303(where n is 2) such that the following operations may be performed toetch a substrate: (1) exposure to fluorine-containing plasma, (2)exposure to Sn(acac)₂ vapor, (3) exposure to fluorine-containing plasma,(4) exposure to Sn(acac)₂ vapor, (5) exposure to hydrogen plasma, and(6) repeat (1)-(5).

FIG. 5 illustrates a method in accordance with the embodiment of FIG. 3,but with the fluorine exposure (operation 501) and the Sn(acac)₂exposure (operation 503) being repeated until n number of cycles havebeen reached (operation 505). Then the hydrogen plasma exposure(operation 507) is performed. The entire sequence is repeated until adesired etch amount is achieved (operation 509).

Disclosed embodiments result in highly controlled etching methods with ahigh degree of uniformity. Disclosed embodiments may be used to performisotropic etching of various materials and may also be modified toperform anisotropic etching by applying a bias at a bias voltage betweenabout 20 V_(b) and about 80 V_(b), such as at about 50 V_(b).

Various embodiments described herein may be performed in a plasma etchchamber such as the Kiyo, available from Lam Research Corporation inFremont, Calif. In various embodiments, a substrate may be shuttledbetween an etching chamber and a vapor chamber without breaking vacuum.

Disclosed embodiments may be performed in any suitable chamber orapparatus, such as the Kiyo® or Flex, both available from Lam ResearchCorporation of Fremont, Calif. In some embodiments, disclosedembodiments may be performed in a cluster tool, which may contain one ormore stations. FIG. 6 illustrates a cluster tool 600, in accordance withimplementations of the disclosure. In various embodiments, one station601 may include a module for etching while another station 603 includesa module for exposing to vapor (e.g., a vapor chamber). In someimplementations, a third station 605 includes a module for exposing to aplasma.

In some embodiments, an inductively coupled plasma (ICP) reactor may beused. Such ICP reactors have also been described in U.S. PatentApplication Publication No. 2014/0170853, filed Dec. 10, 2013, andtitled “IMAGE REVERSAL WITH AHM GAP FILL FOR MULTIPLE PATTERNING,”hereby incorporated by reference for the purpose of describing asuitable ICP reactor for implementation of the techniques describedherein. Although ICP reactors are described herein, in some embodiments,it should be understood that capacitively coupled plasma reactors mayalso be used. With reference to FIG. 7, an example etching chamber orapparatus may include a chamber 701 having a showerhead or nozzle 703for distributing fluorine-containing gases (705), hydrogen gas (707), orSn(acac)₂ vapor (709) or other chemistries to the chamber 701, chamberwalls 711, a chuck 713 for holding a substrate or wafer 715 to beprocessed which may include electrostatic electrodes for chucking anddechucking a wafer and may be electrically charged using an RF powersupply 717, an RF power supply 719 configured to supply power to a coil721 to generate a plasma, and gas flow inlets for inletting gases asdescribed herein. In various embodiments, the chamber walls 711 may befluorine-resistant. For example, the chamber walls 711 may be coatedwith silicon-containing material (such as silicon or silicon oxide) orcarbon-containing material (such as diamond) or combinations thereofsuch that fluorine-containing gases and/or plasma may not etch thechamber walls 711. Modification chemistry gases for chemisorption (suchas fluorine-containing gases for generating fluorine-containing plasma)and/or vapor exposure (such as Sn(acac)₂) may be flowed to the chamber701. In some embodiments, a hydrogen gas 707 may be flowed to thechamber to generate a hydrogen plasma for removing tin or tin oxideresidues. In some implementations, the chamber walls are heated tosupport wall cleaning efficiency with a hydrogen plasma. In someembodiments, an apparatus may include more than one chamber, each ofwhich may be used to etch, deposit, or process substrates. The chamberor apparatus may include a system controller 723 for controlling some orall of the operations of the chamber or apparatus such as modulating thechamber pressure, inert gas flow, plasma power, plasma frequency,reactive gas flow (e.g., fluorine-containing gas, Sn(acac)₂ vapor,etc.); bias power, temperature, vacuum settings; and other processconditions.

FIG. 8 shows a control module 800 for controlling the systems describedabove, in accordance with implementations of the disclosure. Forinstance, the control module 800 may include a processor, memory and oneor more interfaces. The control module 800 may be employed to controldevices in the system based in part on sensed values. For example only,the control module 800 may control one or more of valves 802, filterheaters 804, pumps 806, and other devices 808 based on the sensed valuesand other control parameters. The control module 800 receives the sensedvalues from, for example only, pressure manometers 810, flow meters 812,temperature sensors 814, and/or other sensors 816. The control module800 may also be employed to control process conditions during reactantdelivery and plasma processing. The control module 800 will typicallyinclude one or more memory devices and one or more processors.

The control module 800 may control activities of the reactant deliverysystem and plasma processing apparatus. The control module 800 executescomputer programs including sets of instructions for controlling processtiming, delivery system temperature, pressure differentials across thefilters, valve positions, mixture of gases, chamber pressure, chambertemperature, wafer temperature, RF power levels, wafer ESC or pedestalposition, and other parameters of a particular process. The controlmodule 800 may also monitor the pressure differential and automaticallyswitch vapor reactant delivery from one or more paths to one or moreother paths. Other computer programs stored on memory devices associatedwith the control module 800 may be employed in some embodiments.

Typically there will be a user interface associated with the controlmodule 800. The user interface may include a display 818 (e.g. a displayscreen and/or graphical software displays of the apparatus and/orprocess conditions), and user input devices 820 such as pointingdevices, keyboards, touch screens, microphones, etc.

Computer programs for controlling delivery of reactant, plasmaprocessing and other processes in a process sequence can be written inany conventional computer readable programming language: for example,assembly language, C, C++, Pascal, Fortran or others. Compiled objectcode or script is executed by the processor to perform the tasksidentified in the program.

The control module parameters relate to process conditions such as, forexample, filter pressure differentials, process gas composition and flowrates, temperature, pressure, plasma conditions such as RF power levelsand the low frequency RF frequency, cooling gas pressure, and chamberwall temperature.

The system software may be designed or configured in many differentways. For example, various chamber component subroutines or controlobjects may be written to control operation of the chamber componentsnecessary to carry out the inventive deposition processes. Examples ofprograms or sections of programs for this purpose include substratepositioning code, process gas control code, pressure control code,heater control code, and plasma control code.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe disclosed embodiments. It should be noted that there are manyalternative ways of implementing the processes, systems, and apparatusof the present embodiments. Accordingly, the present embodiments are tobe considered as illustrative and not restrictive, and the embodimentsare not to be limited to the details given herein.

What is claimed is:
 1. A method for performing atomic layer etching(ALE) on a substrate, comprising: (a) performing a surface modificationoperation on a surface of the substrate, the surface modificationoperation configured to convert at least one monolayer of the substratesurface to a modified layer; (b) performing a removal operation on thesubstrate surface, the removal operation configured to remove themodified layer from the substrate surface, wherein removing the modifiedlayer occurs via a ligand exchange reaction that is configured tovolatilize the modified layer, wherein performing the removal operationincludes exposing the substrate surface to a metal complex, such thatthe ligand exchange reaction occurs between the metal complex andconverted species of the modified layer; (c) performing, following theremoval operation, a plasma treatment on the substrate surface, theplasma treatment configured to remove residues generated by the removaloperation from the substrate surface, the residues formed from metalspecies of the metal complex, wherein the residues are volatilized bythe plasma treatment; (d) repeating operations (a) through (c) until apredefined thickness has been etched from the substrate surface.
 2. Themethod of claim 1, wherein performing the surface modification operationincludes exposing the substrate surface to a fluorine-containing plasma,wherein the exposure to the fluorine-containing plasma is configured toconvert the at least one monolayer of the substrate surface to afluoride species.
 3. The method of claim 2, wherein the surface of thesubstrate includes a metal, metal oxide, metal nitride, metal phosphide,metal sulfide, or metal arsenide; wherein the exposure to thefluorine-containing plasma forms a metal fluoride.
 4. The method ofclaim 2, wherein exposing the surface of the substrate to thefluorine-containing plasma includes introducing a fluorine-containinggas into a chamber in which the substrate is disposed, and igniting aplasma.
 5. The method of claim 4, wherein the exposure to thefluorine-containing plasma is performed at a chamber pressure of about10 to 500 mTorr, for a duration less than about 15 seconds.
 6. Themethod of claim 2, wherein performing the removal operation includesexposing the substrate surface to tin-(II) acetylacetonate (Sn(acac)₂)vapor, the exposure to the Sn(acac)₂ vapor being configured to exchangeacac ligands for fluorine atoms in the modified layer.
 7. The method ofclaim 6, wherein exposing the surface of the substrate to the Sn(acac)₂includes introducing the Sn(acac)₂ as a vapor into a chamber in whichthe substrate is disposed.
 8. The method of claim 7, wherein theexposure to the Sn(acac)₂ is performed for a duration of about 1 to 30seconds.
 9. The method of claim 7, wherein exposing the surface of thesubstrate to the hydrogen plasma includes introducing a hydrogen gasinto a chamber in which the substrate is disposed, and igniting aplasma.
 10. The method of claim 9, wherein the exposure to the hydrogenplasma is performed for a duration of about 1 to 30 seconds.
 11. Themethod of claim 6, wherein performing the plasma treatment includesexposing the substrate surface to a hydrogen plasma, the exposure to thehydrogen plasma being configured to volatilize tin, tin fluoride or tinoxide residues on the surface of the substrate.
 12. The method of claim1, wherein operation (a) is performed in a first chamber; whereinoperation (b) is performed in a second chamber.
 13. The method of claim12, wherein operation (c) is performed in the first chamber.
 14. Themethod of claim 12, wherein operation (c) is performed in a thirdchamber.
 15. A method for performing atomic layer etching (ALE) on asubstrate, comprising: (a) performing a surface modification operationon a surface of the substrate, the surface modification operationconfigured to convert at least one monolayer of the substrate surface toa modified layer; (b) performing a removal operation on the substratesurface, the removal operation configured to remove the modified layerfrom the substrate surface, wherein removing the modified layer occursvia a ligand exchange reaction that is configured to volatilize themodified layer, wherein performing the removal operation includesexposing the substrate surface to a metal complex, such that the ligandexchange reaction occurs between the metal complex and converted speciesof the modified layer; (c) repeating operations (a) and (b) for apredefined number of cycles; (d) performing, following operation (c), aplasma treatment on the substrate surface, the plasma treatmentconfigured to remove residues generated by the removal operation fromthe substrate surface, the residues formed from metal species of themetal complex, wherein the residues are volatilized by the plasmatreatment; (e) repeating operations (a) through (d) until a predefinedthickness has been etched from the substrate surface.
 16. The method ofclaim 15, wherein performing the surface modification operation includesexposing the substrate surface to a fluorine-containing plasma, whereinthe exposure to the fluorine-containing plasma is configured to convertthe at least one monolayer of the substrate surface to a fluoridespecies; wherein performing the removal operation includes exposing thesubstrate surface to tin-(II) acetylacetonate (Sn(acac)₂) vapor, theexposure to the Sn(acac)₂ vapor being configured to exchange acacligands for fluorine atoms in the modified layer; wherein performing theplasma treatment includes exposing the substrate surface to a hydrogenplasma, the exposure to the hydrogen plasma being configured tovolatilize tin, tin fluoride or tin oxide residues on the surface of thesubstrate.
 17. The method of claim 16, wherein the surface of thesubstrate includes a metal, metal oxide, metal nitride, metal phosphide,metal sulfide, or metal arsenide; wherein the exposure to thefluorine-containing plasma forms a metal fluoride.
 18. The method ofclaim 16, wherein the exposure to the fluorine-containing plasma isperformed at a chamber pressure of about 10 to 500 mTorr, for a durationless than about 15 seconds; wherein the exposure to the Sn(acac)₂ isperformed for a duration of about 1 to 30 seconds; wherein the exposureto the hydrogen plasma is performed for a duration of about 1 to 30seconds.